Work machines, such as tractors, backhoe loaders, compactors, feller bunchers, forest machines, industrial loaders, skid steer loaders, wheel loaders, mining vehicles, and the like, often employ hydraulic systems that provide functionality and control to various aspects of the machines. Typically, work machines employ multiple fluid pressurizing pumps to provide hydraulic power to a number of different machine functions, including functions pertaining to implement systems, fan drive systems, steering systems, braking systems, propulsion systems, swing systems, and the like.
Based on design choice, the hydraulic system may be configured such that one or more of the machine functions are individually powered by dedicated pumps while other machine functions are powered by a shared pump. For example, while some machines employ a dedicated fan pump configured to only power the fan drive system, other machines often employ the fan pump to drive not only the fan drive system but also the braking and/or steering system. Although sharing a single pump over multiple machine functions may provide more efficient use of the hydraulic system, it does come with its drawbacks.
The fan drive system of a typical work machine is configured to drive the motor of a cooling fan during operation of the machine, which serves to circulate air through air flow passages situated around the engine and dissipate heat from the engine compartment. When the fan pump is used to power the braking and/or steering systems in addition to the fan drive system, power to the fan drive system is sacrificed at the cost of driving the braking and/or steering systems due to the fixed displacement of the fan motor. This reduction in power to the fan drive system results in reduced output torque of the cooling fan, and thus, a reduction in fan speed. Moreover, reductions in fan speed can lead to substantial reductions in engine cooling, which can adversely affect the overall performance and efficiency of the machine.
In addition to cooling the engine, the fan drive system can also be controlled to periodically reverse the rotation of the cooling fan in order to dislodge any debris from screens of the engine compartment which lead to the air flow passages. More specifically, as the cooling fan urges outside air through the screens and into the air flow passages for cooling the engine during normal machine operation, any debris that may be carried by the air can collect on the screens over time, thus hindering air flow and degrading the cooling capabilities of the fan drive system. Various mechanisms have been conventionally used to provide fan reversibility in industrial work machines. In typical implementations, however, angular momentum causes a residual motion in the rotating fan which has been noted to induce vacuums within the hydraulics of the fan drive system. Such vacuums can introduce cavitation within the hydraulics system which can be detrimental to the machine. Additionally, a sudden change in flow direction through valving can cause damaging pressure spikes.
Accordingly, there is a need to improve the overall performance of hydraulic systems in mobile and work machines and reduce parasitic losses. Moreover, there is a need to provide means for controlling and managing hydraulic systems that are better suited to maintain optimum performance of individual machine functions without sacrificing efficiency. There is also a need for improved reversibility of the fan drive system that is less susceptible to pressure spikes caused by pressure differentials within the hydraulic system.